There are various types of integrated circuits which require cooling for optimal operation. One such integrated circuit is an infrared radiation detector. An existing technique for cooling such an integrated circuit is to incorporate a number of thermoelectric cooling elements (TECs) into a package for the integrated circuit.
For example, one known package includes first and second parts which are each thermally conductive and electrically insulating, the first part having the integrated circuit supported on a side thereof opposite from the second part. A plurality of thermoelectric cooling elements are provided between the first and second parts, in thermal engagement therewith. A window which is transparent to infrared radiation is provided at a location spaced from the integrated circuit, on a side of the integrated circuit remote from the first part. A frame extends between and is sealingly secured to peripheral edges of the window and the second part, the first part and the integrated circuit being located within the frame.
The region within the frame and between the window and second part serves as a chamber, which is subject to a vacuum. The second part has a plurality of via openings therethrough which are each filled with a conductive material, and has on each side thereof a plurality of pads which are each aligned with and engage the conductive material in a respective one of the via openings. A plurality of relatively long wirebonds each extend from the integrated circuit to a respective one of the pads on the second part. This known integrated circuit package has been generally adequate for its intended purposes. However, it has not been satisfactory in all respects.
More specifically, the known package cannot be manufactured as inexpensively as is desirable. Further, the wirebonds therein are relatively long, which increases manufacturing difficulties. In addition, the mechanical interconnection between the first and second parts is effected only by the thermoelectric cooling elements disposed therebetween, whereas a stronger mechanical coupling would be advantageous. Another consideration is that, because the TEC elements are disposed in the same chamber as the integrated circuit, and since TEC elements have a tendency to outgas when subjected to a vacuum, it can be difficult to obtain a suitable vacuum within the chamber which includes the integrated circuit. Yet another consideration is that it would be desirable to reduce the size of the package, while obtaining less restrictive manufacturing tolerances, and while providing a package which is easier to manufacture.
Also, some of the TEC elements are n-type elements and others are p-type elements. In the known package they all have the same cross-sectional shape. The n-type elements and the p-type elements are thus visually the same, and can be distinguished only by electrical testing. If n-type and p-type elements become mixed up, the cooling efficiency of the package can be degraded. Consequently, in order to ensure proper assembly, extra care must be exercised on the assembly line, which is tedious and increases the cost of the product.